submit_form_ok should detect non-existent forms instead of accepting them silently.

[forwardever]

it seems that submit_form_ok works without problems even if form fields with the required names do not exist in the form

$mech->submit_form_ok({
    form_number => 1,
    fields      => {
        password                => 'test',
        password_confirm        => 'test'
    }
});

but fields in the form are named password1 and password_confirm1